1. Field of the Invention
This invention relates to a method for measuring the amount of chlorophyll and also to a chlorophyll meter, and more particularly to a method of optically measuring the amount of chlorophyll of living leaves and a meter for measuring the same.
2. Description of the Prior Art
It is known in the art that the spectroscopic absorption shows the maximum absorption at about 670 nm and the constant minimum absorption in the range over 750 nm. The maximum absorption is caused by absorption by chlorophyll and the minimum absorption has nothing to do with chlorophyll.
By utilizing the spectoscopic absorption as above, it is known to measure the amount of chlorophyll contained in the leaves. It is mentioned in Proceedings of the Corp Science Society of Japan, Vol. 17, pages 158-162.
The conventional chlorophyll meter disclosed in the above document is provided with two interference filters having the principal wavelength of 670 nm and 750 nm, respectively. This meter first measures the light passing through the leaves through the interference filter of the principal wavelength of 750 nm to obtain the long wavelength region light by use of a CdS photodetector and sets the meter at zero point with the output of the photodetector obtained at this stage. Then, the filter is changed to the other one having the principal wavelength of 670 nm to measure the light passing through the leaves by use of the CdS photodetector. The output of the photodetector obtained at this stage is displayed by the meter to indicate the amount of chlorophyll of the leaves to be measured.
The above mentioned chlorophyll meter is advantageous in that the amount of chlorophyll can be measured by comparing the maximum transmission density and the minimum transmission density of the living leaves. However, it is disadvantageous in that the transmission density or the amount of light passing through the leaves must be measured twice, which results in a long measuring time and troublesome handling of the interference filters to be changed and also a complicated circuitry to measure the two outputs and compare the same.